You may have imported your contacts and you now need to add your contacts into new groups in bulk...
1. Export your contacts to .csv file which will also give you the unique identifier of Contact ID number in the left column.
2. Copy/paste your contacts into appropriate separate spreadsheets to suit your groups.
3. Action update imports during which you have the option of using either email address (if all your contacts have a valid email address) or Contact ID in the duplicate processing section. (also match the key fields in the top section such as First Name, last Name, Contact ID, Email address)
4. In the Groups section tick the new group option and type the name of your new group in the box provided.
That will create new groups for your segmentation and avoid duplicate contacts.
If you have further questions about this please search our Support site or raise a Support ticket to us.